Gap Anisotropy, Spin Fluctuations and Normal-State Properties of the Electron Doped Superconductor Sr0.9La0.1CuO2

Abstract

We report the results from a thermopower and a Cu nuclear magnetic resonance (NMR) study of the infinite CuO2 layer electron doped high temperature superconducting cuprate (HTSC), Sr0.9La0.1CuO2. We find that the temperature dependence of the thermopower, S(T), is different from that observed in the hole doped HTSC. In particular, we find that dS(T)/dT is positive above ~120 K. However, we show that S(T) can still be described by the same model developed for the hole doped HTSC and hence S(T) is not anomalous and does not imply phonon mediated pairing as has previously been suggested. The Cu NMR data reveal a Knight shift and spin lattice relaxation rate below Tc that are inconsistent with isotropic s-wave pairing. The Cu spin lattice relaxation rate in the normal state, however, is Curie-Weiss like and is comparable to that of the optimally and overdoped hole doped HTSC, La2-xSrxCuO4. The magnitude of the Knight shift indicates that the density of states at the Fermi level is anomalously small when compared with the hole doped HTSC with the same Tc, indicating that the size of the density of states at the Fermi level is of little importance in the HTSC. We find no evidence of the normal state pseudogap that is observed in the hole doped HTSC and which was recently reported to exist in the electron doped HTSC, Nd1.85Ce0.15CuO4, from infrared reflectance measurements.